It doesn't really solve that use case though, does it?
Eg, IPFS isn't permanent hosting - it's purely hosting as long as there are seeds, like bittorrent. Hypothetically if a package is very old there may be no seeds for it anywhere. Someone (NIXOS/etc) will still have to pay for hosting.
It does provide a solution though. If someone is still hosting it, you can access it in the same way. Nobody can pull, independently, a specific version down. They could remove their copy and hope nobody else is also providing it, but if it was a big problem other people could quickly start providing it and nobody else would notice the difference.
Perhaps an equivalent thing for "someone will still have to pay for hosting" is that although that's true, anyone can put money into the pot to keep it going or bring it back, it's not reliant on the original creator to keep paying for it.
Eg, IPFS isn't permanent hosting - it's purely hosting as long as there are seeds, like bittorrent. Hypothetically if a package is very old there may be no seeds for it anywhere. Someone (NIXOS/etc) will still have to pay for hosting.